The present invention relates to a cassette of the kind that holds x-ray film sheet while the sheet is exposed.
It is known to provide x-ray film cassettes having means for identifying certain attributes of the cassette, film or the like. For example, U.S. Pat. No. 3,942,016, which issued Mar. 2, 1976, discloses an x-ray film cassette which has color coded disks in two edges thereof. The purpose of the coded disk is to identify a property of the film, such as the film speed.
It is also known from U.S. Pat. No. 4,903,288, issued Feb. 20, 1990, to provide an x-ray film cassette with a visual indicator which enables an operator to determine whether the film in the cassette has been exposed or is unexposed. More specifically, a device attached to the film cassette includes a phosphor screen which fluoresces on exposure to x-radiation. A photo cell detects light emitted by the screen and generates a control signal which alters the status of a liquid crystal display from a first condition, which indicates that the film is unexposed, to a second condition, which indicates that exposure of the film has occurred. The device requires an electronic circuit, a fluorescent screen and a detector which makes the device expensive to implement and also requires space within or on a cassette for holding the device.
With most x-ray film cassettes commonly in use, there is no way to distinguish between cassettes containing unexposed film and those cassettes containing exposed film. As a result, cassettes with exposed film can inadvertently be exposed a second time while cassettes containing unexposed film which the operator mistakenly believes has been exposed may be developed with no image thereon. In either case, the sheets of film are lost. This is not only costly, but patients will need to be exposed to x-radiation a second time in order to obtain a radiograph.
Portable x-ray units are used in hospitals to obtain radiographs of patients that cannot easily be transported to the radiography department. Sometimes a bin for x-ray cassettes is provided on a portable x-ray unit to carry cassettes having exposed film and also cassettes having unexposed film. In some cases the operator of the x-ray unit uses a movable partition in the bin to separate cassettes containing exposed film from cassettes containing unexposed film. However, errors still occur. For example, in low light conditions often encountered in a patient's room, it is difficult for the operator to see the partition so cassettes can be placed on the wrong side of the partition after exposure or removed from the wrong side of the partition before exposure. Also, different operators of a portable unit do not always place exposed cassettes on the same side of the partition, i.e., some place them on the front side of the partition while others place them on the back side of the partition. Thus, when two x-ray technicians are working together, there is a potential for improper placement of cassettes containing exposed and unexposed film.